Violentmonkey provides userscripts support for browsers. It works on browsers with WebExtensions support.
Example Firefox add-ons created using the WebExtensions API
Tree Style Tab, Show tabs like a tree.
A command line tool to help build, run, and test web extensions
An awesome browser extension that reads aloud webpage content with one click
Some web pages use intermediary pages before redirecting to a final page. This add-on tries to extract the final url from the intermediary url and goes there straight away if successful.